The present invention relates to a biomagnetic measurement technique detecting a very weak magnetic field such as a magnetocardiogram and a magnetoencephalogram using an SQUID (superconducting quantum interference device) magnetometer as a superconducting device.
An action potential occurs by excitation of a ventricular muscle to produce a very weak electric current in the ventricular muscle in appearance. Along with the electric current, a very weak magnetic field is produced outside a living body. The very weak magnetic field from a heart (hereinafter, abbreviated as a “magnetocardiogram”) is measured using a highly sensitive magnetic sensor called a superconducting quantum interference device (SQUID). The magnetocardiogram is less affected by the conductivity of a living body, which is hard to be subject to waveform distortion. From the measurement result of the magnetocardiogram, an attempt to image an electric current activity on the surface of a ventricular muscle has been made.
In the attempt to image an electric current activity, there is proposed a method for calculating Ix=dBz/dy and Iy=−dBz/dx from a magnetic field (Bz) of a vertical (z) element to the surface of a living body to reconstruct a distribution of imaginary current vectors I=(Ix, Iy) (for example, see Japanese Patent Application Laid-Open No. 10-248821).
As an ischemic area identification method, there is proposed a method for calculating the total of absolute values of the imaginary current vectors I in a predetermined period (for example, see Japanese Patent Application Laid-Open Nos. 10-305019 and 11-151221). An ischemic area is estimated by mapping of the total value in the predetermined period.
As an invasive method for directly measuring a ventricular muscle action potential, there is catheter mapping. The catheter mapping is a method for directly contacting a catheter having at its edge a plurality of potential measurement electrodes with the inner surface of a heart to measure a ventricular muscle action potential.